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Investments accounted for using equity method - Details of Investment in Associates (Detail) - TWD ($) $ in Thousands		12 Months Ended
	Apr. 08, 2019	Dec. 31, 2020	Dec. 31, 2019
Disclosure of associates [line items]
Carrying amount		$ 3,271,677	$ 3,392,910
JMC ELECTRONICS CO., LTD. [member]
Disclosure of associates [line items]
Carrying amount		$ 250,769	249,793
Shareholding ratio	10.00%
Unimos Shanghai [member]
Disclosure of associates [line items]
Principal place of business		Shanghai, PRC
Measurement method		Equity method
Carrying amount		$ 3,020,908	$ 3,143,117
Shareholding ratio		45.02%	45.02%
Nature of relationship		Strategic Investee

X

- Definition

The country in which an associate of the entity is incorporated. [Refer: Associates [member]]

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- Definition

The description of the nature of the entity's relationship with an associate (for example, describing the nature of the activities of the associate and whether they are strategic to the entity's activities). [Refer: Associates [member]]

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The description of whether the investment in an associate is measured using the equity method or at fair value. [Refer: At fair value [member]; Associates [member]]

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The amount of investments in associates accounted for using the equity method. [Refer: Associates [member]; Investments accounted for using equity method]

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